Water comes up other sink when disposal is on

We have been battling this problem for years now. Both kitchen sink sides drain freely. But...if there is water in the disposal side and the disposal is turned on, there is bubbling and gurgling on the disposal side and water comes up into the other sink. Any ideas?

It the drains are really ok, then to some extent this may just be the nature of your installation. The disposer acts as sort of a pump, and as it send the water out, that water will look for the path of least resistance, and will often split between going down the drain and going across to the other sink.

If you could post a picture of the piping under the sink, this could be made clear.

We have been battling this problem for years now. Both kitchen sink sides drain freely. But...if there is water in the disposal side and the disposal is turned on, there is bubbling and gurgling on the disposal side and water comes up into the other sink. Any ideas?

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Do a small test, fill up the side without the disposal. Fill it all the way up. Then let it drain and observe what happens on the disposal side. If it backs up into the other side while it is draining then there is a partial blockage.

See most people just run the water in both sides and it will drain just fine, but when you fill a side up and let the water go, you are getting a flow rate greater than what the faucet can supply and it will help you diagnose the issue. Now if it does not back up when you drain that side of the sink. The problem is in how its piped under the sink. Then a picture will be a great help.

Do a small test, fill up the side without the disposal. Fill it all the way up. Then let it drain and observe what happens on the disposal side. If it backs up into the other side while it is draining then there is a partial blockage.

See most people just run the water in both sides and it will drain just fine, but when you fill a side up and let the water go, you are getting a flow rate greater than what the faucet can supply and it will help you diagnose the issue. Now if it does not back up when you drain that side of the sink. The problem is in how its piped under the sink. Then a picture will be a great help.

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Water comes to the top of the disposal side when a full sink is released from non-disposal side. No gurgling and bubbling. I'm including a photo of the plumbing, but I suspect our 34-year old pipes need a good goosing!

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Well yes you have a slow drain, a good power rodding will fix that, then second you need to repipe under your sink. that corrugated pipe needs to go, Also they make a disposal kit for end waste discharge that will get rid of the down turned pipe. Below are some pictures. The tee should have a baffle in it as well.

If you are in Illinois you are not allowed to use a single trap for both sides of the the sink and are not allowed to discharge the dishwasher into the garbage disposal. If you are in Illinois let me know and I will post pics on how it should be installed to meet Illinois code.

Thanks for the offer...we live in Tucson, AZ. My husband had a heck of a time installing our sink and disposal after our kitchen remodel. The new sink is larger than the old one and the drains did not match up with the existing plumbing. After several tries with various piping and connections, he was forced to use that stupid flex stuff, which he hates! From the photo, would you have a suggestion as to how we can eliminate the flex and use rigid?

We knew you would say that. My husband has avoided that solution from day one. For the record, I have urged him to bring in a real plumber but he is a glutton for punishment...and loves doing things himself.

I should mention that earlier this week we borrowed an electric snake from a friend and ran it from the beginning of the line outside the sink all the way to our septic tank...twice. It went through very easily the second pass. If we have a blockage it may be in that pesky pipe or between it and and where we started the snaking. Our next task will be to check that pipe and clear it if there is blockage. I will let you know how we fair. Thanks again.

There is a couple of things Illinois wants done and not done. First they do not want you to discharge the dish washer into the disposal and the other thing is they want the disposal to have its own trap separate from the other side of the sink.

Below is from the Illinois plumbing code book.

Section 890.710 Food Waste Disposal Units

a) Installation. Food waste disposal units shall be trapped separately from any other fixture or compartment, shall be connected directly to the sanitary drainage system, and shall be properly vented. Dishwashers shall not discharge into food waste disposal units. Units may have either automatic or hand-operated water supply control. (See Section 890.1130(a), (b) and (c).)

a) Domestic Dishwasher (Private Residence). When a domestic dishwashing machine drain line is connected to the house side of a trap from a sink, the drain from the dishwasher shall be carried up to the underside of the spill rim of the sink. Dishwashing machines shall discharge separately into a trap or tail piece of the kitchen sink and shall not connect to the food waste disposal unit.

b) Water Supply Connection. The water supply to commercial dishwashing machines shall be connected through an air gap or by means of proper backflow protection, e.g., a non-pressure type (atmospheric) vacuum breaker or a dual check valve backflow preventer assembly (DuC), depending upon the circumstances.

c) Commercial dishwashing machines shall indirectly discharge to a proper receptor connected to the drainage system or as permitted in Section 890.1010(a).

d) Hot Water. A commercial dishwashing machine or similar dishwashing equipment that relies upon hot water for sanitizing dishes and utensils, rather than chemicals for sanitizing, shall provide rinse water at 180 degrees F., except for a single-tank, stationary-rack, single temperature dishwashing machine which shall provide a rinse water temperature of 165 degrees F., in accordance with Section 750.830(h) of the "Food Service Sanitation Code" (77 Ill. Adm. Code 750). ​

Let me post this part of the code about trap venting. So the other pro's will not say that this picture is wrong. The part in red is what pertains to the use of two traps on one vent under the kitchen sink. The picture is also from the plumbing code book. I am trying to find a better pic or drawing.

b) Common Vent. A common vent, installed vertically, may be used for two fixture traps when both traps connect with a vertical waste at the same level. (See Appendix K: Illustration O.)

c) Vertical Wet Vent. A vertical wet vent may be used for two fixtures set on the same floor level, but connecting at different levels in the stack, provided the vertical drain is one (1) pipe diameter larger than the upper fixture drain and that both drains conform to Appendix A: Table I. (See Appendix K: Illustrations P and Q.)

OK had to borrow a picture another poster used to show how they installed their sink , disposal and drain pipes. So it should look like this in Illinois. The only difference is they want you to use a double wye and have each trap coming of each part of the wye , and put a clean out adapter in the center pipe. As shown in the badly drawn illustration in the upper post.

Apparently Illinois' code has gone downhill since I was there, unless that is different from the Chicago code. As an aside, that disposer trap is NOT properly vented, especially if it goes into a lateral arm which then goes to a vertical pipe. The disposer discharge, being from a "pump" can create enough velocity to cause a siphon past the second trap's outlet and deplete the trap seal. The problem with the lady's installation is that the tee is a simple straight slip tee, NOT a baffle tee, so excessive water is not forced to go down to the trap, but can backflow up to the sink when it hits the back of the tee. If she were in Phoenix, any of us plumbers could correct it, and get rid of the Mickey Mouse flexible pipe in the process.

Apparently Illinois' code has gone downhill since I was there, unless that is different from the Chicago code. As an aside, that disposer trap is NOT properly vented, especially if it goes into a lateral arm which then goes to a vertical pipe. The disposer discharge, being from a "pump" can create enough velocity to cause a siphon past the second trap's outlet and deplete the trap seal. The problem with the lady's installation is that the tee is a simple straight slip tee, NOT a baffle tee, so excessive water is not forced to go down to the trap, but can backflow up to the sink when it hits the back of the tee. If she were in Phoenix, any of us plumbers could correct it, and get rid of the Mickey Mouse flexible pipe in the process.

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HJ if you look at this illustration that the Illinois Plumbing code points to It shows a double wye fitting with a clean out installed in the middle. Also the code allows for two traps to be used on a common vent as long as they enter the pipe at an equal level, and the vent is installed vertically.

b) Common Vent. A common vent, installed vertically, may be used for two fixture traps when both traps connect with a vertical waste at the same level.

Also some where in the code they say this arrangement is only allowed on the kitchen sink. I will go digging for it in a bit and post the section.

Well also I am posting what is allowed in Illinois. You should know the State's code is the bare minimum allowed. Counties, townships, and cities can make the code stricter but not less strict than the State code.

In Chicago they want the p-traps installed like this when using a common vent for the kitchen sink. They still do not want the disposal and the sink basin on a single trap since that would be less strict than the State code, as well as the dishwasher either has to be installed on its own trap or on the tail-piece for the side with out the disposal.